Neutronic reactor system



i through a are typical moderatorssuitable for such use.

Patented June 9, 1964 3,136,699 NEUTRONC REACTOR SYSTEM Walter H. Zinn,Chicago, Ill., assignor to the United States of America as representedby the United States Atomic Energy Commission Filed Feb. 21, 1946, Ser.No. 649,399 1 Claim. (Cl. 176-28) This invention relates to neutronicreactors and more particularly to a novel meansfor cooling thefissionable material within such a reactor by circulating said materialbody of coolant disposed externally of the reactor.

In neutronic reactors a thermal neutron iissionable (herein calledfissionable, as is common in the art) isotope such as Um, U235, or 94239or mixtures thereof is subjected to fission by absorption of neutronsand a selfsustaining chain reaction is established by the neutronsevolved by the fission. In general such reactors comprise bodies ofcompositions containing fissionable material such, for example, asnatural uranium, disposedl in a neutron slowing materialwhich slows theneutrons to thermal energies. Such a slowing material is termed aneutron moderator. Graphite, beryllium, and D20 (heavy water)Accordingly, the term moderator as used both in the specification and inthe claim, be understood to have the meaning commonly assigned to it inthe nuclear reactor art, that is, as referring to materialspredominantly containing elements of atomic .weight of 16 or less. Heatis evolved during the reaction which must be removed in order tomaintain stable temperature conditions in the reactor. Y Specificdetails ofthe theory and essential characteristics of such reactors areset forth in coperiding application of Enrico Fermi and Leo Szilard,Serial No. 568,904, filed December 19,` 1944, now Patent No. 2,708,-

1n neutronic reactors the ratio of the fast neutrons produced in onegeneration by the fissions to the original number of fast neutrons in atheoretical system of infinite size where there can be no external lossof neutrons is called the reproduction or multiplication factor orconstant of the system, and is denoted by the symbol K. For any finitesystem, some neutrons will escape from the periphery of the system.Consequently a system of finite size may be said to have a K constant,even though the value thereof would only exist if the system as builtwere extended to infinity without change of geometry or materials. Thuswhen K is referred to herein as a constant of a system of practicalsize, it always refers to what would exist in the same type of system ofinfinite size. 1f K can be made sufficiently greater than unity toindicate a net gain in neutrons in the theoretical system of infinitesize, and then. an actual system is built to be sufficiently large sothat this gain is not entirely lost by leakage from the exterior surfaceof the system, then a self-sustaining chain reacting system of finiteand practical size can be built to produce power and related by-productsby nuclear fission of natural uranium. The neutron reproduction ratio ina system of finite size, therefore, diiers from K by the externalleakage factor, and by a factor due to the neutron absorption oflocalized neutron absorbers, and the reproduction ratio must still besufficiently greater than unity to permit the neutron density to riseexponentially with time in the system as built.

During the interchange of neutrons in a system of finite size,comprising bodies of any size disposed in a neutron moderator, neutronsmay be lost to the chain reaction in four ways:

of the bodies without producing fission;

By absorption or capture in the uranium content (2) By absorption orcapture in the moderator material itself;

(3) By absorption or capture by the impurities present l in both theuraniumrbodies and in the moderator; and

(4) By leakage out of the system through the periphery thereof.

The present invention is particularly concerned with the removal of heatfrom the reactor. A general object of the invention is to provide anovel method and means for cooling sol'd fissionable material within aneutronic reactor. by circulating said material through a body of fluidcoolant disposed externally of the reactor. l

A more spec'fic object of the invention is to provide a reactor such asabove described comprising elongated members moving into and out oftheneutron moderator and' containing fissionable material, said membersbeing cooled externally of said moderator.

Another object of the invention is to provide endless flexible memberscontaining iissionable material,f and means for moving said membersthrough adjacent bodies of neutron moderator and a coolant.V

Still another, object of the invention is to designa neutronic reactorwherein the fissionable material is in the form of endless chainscirculated as by sprockets through the neutron moderator and throughcooling means disposed externally thereof. The foregoing and otherobjects and advantages of the invention will become apparent from aconsideration i of the accompanying specification and the drawingswhere- FIG. l is a diagrammatic, central, vertical sectional view takenthrough 'a structure embodying the invention, portions of the structurebeing shown in elevationg/ FlG. 2 is a transverse vertical sectionalview takeri in the plane indicated by line 2--2 of FlG. 1',

FIG. 3 is a fragmentary side elevationalview of one of the reactivechains shown in FlG. 4l; and

FlG. 4 is a top plan view of the chain shown in FIG. 3.

The neutronic reactor generally designated 2 is disposed within aconcrete vault comprising top and bottom walls 4 and 6, and end walls 8and 10, side walls 12 and 14 and a horizontal wall or ledge 16 extendingbetween the side walls 12 and 14 and spaced from the walls 8 and 10,said vault being adapted to absorb biologically harmful ernanations,such as neutrons and alpha, beta and gamma rays.

The reactor 2 comprises a mass of neutron moderator 18, such as graphiteor beryllium with longitudinal passages 20 extending therethrough, saidmoderator being supported by ledge 16. Endless chains 22, containingiissionable material, and constructed as hereinafter more particularlydescribed, circulated as by sprockets 24 through the passages 2.0 andthrough a tank 26 containing a suitable coolant, such as ordinary watercirculated through the tank by inlet and outlet pipes 27 and 29. Thesprockets are rotated by shafts 31 mounted in conventional bearings(FIG. 2) and connected to any suitable actuating means (not shown)adapted to rotate said shafts.

It will be understood that the portion of the chains 22 within theneutron moderator 1S are effective to produce a nuclear fission chainreaction, inasmuch as the moderator is effective to slow neutrons Withinthe system to thermal energies at which they are most effective tofission the iissionable material within the chains 22. The coolantwithin the tank 26 is preferably a substance such as ordinary waterhaving a greater neutron capture cross section than that of themoderator 18, whereby a chain reaction in the tank 26 is prevented.

The reaction is controlled to maintain any desired neutron densitywithin the reactor 2 by a control rod 28 adapt- Y ed to reciprocateWithin `an aluminum tube 30 extendingv Yoi" the invention except insofaras included inthe accominto the moderator 18. The rod'is actuated by varack panying claim.v l Y Y g I n 1 t ,and pinion mechanism 32 and theneutron density n the What is claimed is: t i Y l Y reactor may bemonitored by any conventional control A neutronic reactor systemcomprising al vault adapta means (not shown). Y d i Y d 5 ed toY absoibVbiologicallyharmful radiations Va ledge Referring now lto FIGS. 3 and.4, it will be seen that traversing'the vault, a mass of graphite havinglongitudieach chain 22 is composed of fluid tight cartridges or coiinalpassages therethrough and being of lesser length than tainers 33 formedof neutron permeable material such as t t e interior of the vaultsupported on the ledge a tank Y connecting links form an endlesschainas'shown in FIGS. 20 p0rt0`1110f said chain Withinsaid mass 'bei'ngsolJcon- 3,136,699. y ,I 'i

taining a'slug or pellet 34V of-ssionable material," pref- 10 outletpipes connectedto and'rextendingthrough erably in the form ofv aplutonium alloy or compound VWalls of the vault, and adapted tocirculate ordinary Water or in the form of uranium having a natural orenriched jthrough the tank, shafts Journalled transversely of theisotopic content of fssionable U235 `If desired, alternate vault vin theregions adjacent to the ends of the mass of cartridges may contain slugsor pellets 34. formed of Yneugraphite, sprockets mounted on the shaftsopposite the tron moderator, such as berylliumor graphite 15 ends yofthe passages, and endless chains comprising fluid- Each cartridge 33 isprovided with a pair of lugs 35 tight cartridges of aluminum eachcontaining a body of welded thereto at each end thereof the lugs at eachend of.V uranium, said chains being mounted on the sprockets to eachcartridge being pivoted at 36 as by rivets to connect#M e dllVellthereby and haVlIlg the depending POI H0115 and v i, K Vstructedlandfarranged as toV undergo a self-sustaining 1 he amounts of neutronmoderator andssionable maf' neutronic reactiong,Y 1 *Y I ,1 Y 1- terialnecessary to sustainV a chain reaction in a reactor Y i Y i 1 v, f .I vi y Y such yas that vaboveV described-'rare fully disclosed in said,Y f"Refeences Cited 111 the lepof hlS Raten? copending applic'atiomand itwill be understood that by 25 'l f. UNITED STATES vPATENTS enriching themembers 34Jso that they contain'la greater Y 876 183? I Ier'd(` Y ,Y YJ`an 'V77 71908 Y isotopi'econtent of ssionablemateri'al than theisotopic.V Y v '896251 Y'Iil'mn'lpson Y Jung 941908 content of U235innatural uranium, the size of an operative 13955072@ Fenton etal 1 r 4 7Jai 24 V1933 n' Y reactor may be considerably reducedbelow that required2,708 656 f Y Fermi t aL My 17 1955 l'for anatural uranium reactor,vprov'idedthat neutronic 30 V7365595 'Wgherlet al. Y Feb;V 2851956 Y, iimpurities, having relatively great'neutron capture cross- Y I f Ysections, are substantially eliminated, as more fully disv QREIGNPATENTS Y cussed in said copending-application. ,1, f Y i, 233,0l1"SWZCIlaVIld '',Q Oct. 2, 1944 Although'the abovedis'cussed theory ofnuclear ire- 35 233,278 Swltzerlanrdij-ne---u Oct 16 1944, action isbasedfon the best experimental evidence knownY y' lastrci--f-e-----/g'yzg kat present, it will be understood that experimental data. Y114,151 ,t v Australia -L---WMaylsp H1940( -tion has been described withrespect tothe specific details 40m Keus/.nt 1 -p phy, Rev, 73, VV1135-9V(1948i. of certain embodiments, thereof, it is not intended that ySmyth:-Atomi`cEnergy for Military Purposes, August YYvoTiiaRfRisisisiznriciss,v

such details shall be regarded as limitations upon the scope j 1945pp.103 and 104; page 23.

